DPR's DR results for both 5D3 and D800 have been out. So, now we can compare against the K-5:-
http://www.dpreview.com/reviews/pentaxk5/14
(Select the cameras and the settings in the second comparison tool boxes)
Note that the DPR DR measurement is a real-life approach to shoot a greyscale target in EV steps and check what the cameras can deliver all by themselves, with different in-camera settings.
So, the above results are self-explanatory by themselves. At the end of the day, the DR of 5D3 and D800 are still wider and they are better, no matter what and how it is compared.